Extensible On-Demand Property System

1. A computer-implemented method for managing properties of objects, the method comprising: associating an expression with a property of an object, the expression defining a relationship between the property and at least one source property; in response to a request for a value of the property, evaluating the expression to determine the value of the property; returning the value of the property; invalidating the value of the property if the at least one source property has undergone a change; and reevaluating the expression to determine a new value of the property based on the change to the at least one source property in response to a subsequent request for the value of the property.

2. The computer-implemented method of claim 1 , wherein the relationship defined by the expression corresponds to a relationship between a value of the at least one source property and the value of the property.

3. The computer-implemented method of claim 2 , wherein evaluating the expression comprises determining the value of the at least one source property to compute the value of the property.

4. The computer-implemented method of claim 3 , wherein the value of the at least one source property is defined by another expression.

5. The computer-implemented method of claim 1 , wherein invalidating comprises clearing the value of the property from a cache.

6. The computer-implemented method of claim 1 , further comprising invalidating other property values that are defined by other expressions and for which the property is a source in response to a change in the value of the property.

7. The computer-implemented method of claim 6 , further comprising monitoring the at least one other property being invalidated to determine whether a circularity exists within the relationship.

8. A computer-implemented method for managing properties of objects, the method comprising: associating an expression with a property of an object, the expression defining a relationship between the property and at least one source property; in response to a request for a value of the property, evaluating the expression to determine the value of the property; returning the value of the property; invalidating other property values that are defined by other expressions and for which the property is a source in response to a change in the value of the property; and monitoring the at least one other property being invalidated to determine whether a circularity exists within the relationship.

9. The computer-implemented method of claim 8 , wherein the relationship defined by the expression corresponds to a relationship between value of the at least one source property and the value of the property.

10. The computer-implemented method of claim 9 , wherein evaluating the expression comprises determining the value of the at least one source property to compute the value of the property.

11. The computer-implemented method of claim 10 , wherein the value of the at least one source property is defined by another expression.

12. The computer-implemented method of claim 8 , further comprising invalidating the value of the property if the at least one source property has undergone a change.

13. The computer-implemented method of claim 12 , further comprising reevaluating the expression to determine a new value of the property based on the change to the at least one source property in response to a subsequent request for the value of the property.

14. The computer-implemented method of claim 12 , wherein invalidating the value of the property comprises clearing the value of the property from a cache.